Regenerative tiptoe incinerators, also called regenerative thermal oxidizers, receive air or gas containing volatile organic compounds, VOC's. The gas is heated in a regenerator bed packed with ceramic pieces. At the hot end of the bed, fuel and air are added thru a burner to heat the gas up to the range of 1400 to 1800 deg. F. At this temperature, the VOC's are oxidized to CO2 and H2O by the oxygen present. The hot purified gas then enters one of the other regenerators where the gas is cooled and discharged from the system. At intervals the gas flow is reversed so that each bed is alternately cooled and heated. To improve the gas purification, a third bed is used so that the feed bed can be purged with clean gas before being used as an exit bed.
The three bed arrangement, which is the standard in the industry, is shown, for instance, in FIG. 1 of the attached drawings and in Houston U.S. Pat. No. 5,026,277. Unfortunately, six large powered valves, plus 3 smaller powered valves for the purge, are required in these prior art systems. For large regenerators, it is common to use live, or even 7, beds. When using five beds, two beds receive feed gases, two beds are used for exit gases and one bed receives purge gases. With such a system, 15 powered valves are required. Since the feed and exhaust ducts are often 4 feet or more in diameter, the valves are very expensive. Operation of the many valves requires an extensive computer system to open and close the valves at the correct moment and to indicate the actual valve position. Continued good maintenance is required since a leaky main valve will allow impure feed gas to flow directly into the purified exit gas. Large rotary valves heretofore used for controlling hot incinerator gases have leakage problems caused by thermal expansion of the valve components. The edges of the rotor cannot seal tightly against the inside of the valve body while allowing the rotor to move easily. The impure feed gas is at a higher pressure than the exit gas so leakage along the outside of the rotor allows impurities to get into the exit gas.